An exploratory well being drilled on the North Slope by the Spanish oil company Repsol suffered an apparent blowout Wednesday morning when drillers were unable to control pressure from a pocket of natural gas, state and company officials said.

Drilling mud and methane gas shot from the well through a diverter pipe, but none of the 76 workers on the rig were injured, no oil was spilled and the gas didn't ignite, the officials said.

The well spewed gas for hours Wednesday, but by about 5:45 p.m. the gas had stopped flowing on its own, indicating it was probably from a small pocket, said Dan Seamount, chairman of the Alaska Oil and Gas Conservation Commission. The well was still producing water and remained out of control, he said.

A well-control contractor mobilized from a field office in Anchorage and its headquarters in Texas and was expected to be on site by early today, Seamount said.

A spokesman for the Alaska Department of Environmental Conservation, Ty Keltner, said drilling mud landed on the rig and neighboring snow. The DEC initially said the spill contained about 1,200 gallons of drilling mud, but by 7:30 p.m. had increased the estimate to about 42,000 gallons, based on information from Repsol.

Drilling mud is a clay mixture designed to lubricate the hole, carry cut rock to the surface and provide downward pressure to reduce the risk of a blowout.

Officials identified the well as Qugruk 2 or Q2. It was on land on the Colville River delta about 1 3/4 miles from the Arctic coastline and about 55 miles west-northwest of Deadhorse, Seamount said. The nearest village, Nuiqsuit, is about 18 miles away.

The blowout occurred as a group of Repsol-North America officials were visiting the North Slope. The Madrid-based company, a big player in the international oil business, only recently came to Alaska. Its announcement last year that it would begin an aggressive exploration program this winter was cheered by state officials and legislators interested in diversifying Alaska's North Slope industry and in boosting total production.

But Pamela Miller of the Northern Alaska Environmental Center said it was sobering to note that Repsol had more than 100 offshore leases in the Chukchi Sea, making it second only to Shell. Environmentalists have expressed concern about the effects of a well blowout in the Arctic Ocean, where spilled oil would be difficult to contain.

One of the visiting Repsol officials was Jan Sieving, the company's North American vice president for public affairs, who was called upon to deal with the crisis from an oil camp with a cell phone that barely worked.

Sieving said the rig contractor was Nabors Alaska Drilling. When the blowout occurred about 9 a.m., the workers were evacuated and the rig shut down, she said.

Seamount, in Juneau for hearings and meetings with legislators, said because the rig was "cold," there was not likely to be an ignition source that could cause the gas to explode.

Repsol hired Wild Well Control of Houston, with an Anchorage office, to restore control. Seamount said it's likely they will force heavy "kill-weight mud" back down the well.

Advances in drilling technology and geologic modeling have reduced blowouts, but not eliminated them, as the BP disaster in the Gulf of Mexico shows.

"Blowouts are exceedingly rare," Seamount said in an email message. Since 1949, Alaska's 7,553 wells have generated 19 blowouts. None have resulted in oil spills on tundra or water, he said. Before Wednesday, the last blowout on the North Slope was in 1994 in the Endicott field, he said.

At Q2 Wednesday morning, with the temperature around 14 below and areas of low fog hanging around the rig, workers were pulling the drill out of the well, a routine operation, when "they had a gas kick," Seamount said. The well was about 2,525 feet deep at that point, on its way to a planned 7,000 feet.

Mud and gas shot out of the well. Drillers responded by pumping more mud down the hole in an attempt to kill it, the DEC said. But the new mud was blown out too.

"The diverter worked the way it's supposed to," Seamount said. "All the personnel got out of the way."

In the early stages of a well like Q2, drillers don't use the heavy blowout preventers that the world learned about from the Gulf of Mexico disaster. Instead, Seamount said, surface holes rely on diverters to route mud, gas, oil and water safely away from the rig in the event of a blowout. The diverter vent on Q2 was about 75 feet from the rig, Seamount said.

Pressurized gas pockets are common hazards of drilling.

"We are not sure why they lost control but will pursue that as part of our incident investigation," Seamount said. An inspector from his agency was on the scene Wednesday and the DEC expected to have four representatives there Thursday.

Even if no oil spilled as a result of the lost well control, "it's going to be a very expensive incident for Repsol," Seamount said. Well-control contractors don't come cheap, he said, and the Nabors rig will be idle for some time.

Repsol has attracted attention in Congress recently because it is drilling several deepwater exploratory wells in Cuban waters not far from U.S. territorial water off Florida.

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